In the case of dyeing fibers including cellulosic or nitrogen-containing fibers, use is usually made of water-soluble reactive dyes. For such reactive dye, demands are on those dyes which have excellent levelling property, are capable of dyeing fiber materials to be dyed with high density, and yet prossess favorable color fastness of the dyed articles to various circumstances. The characteristics of such reactive dyes differ delicately by the basic skeletal structure, substituents, reactive groups, and their combination, on account of which there have so far been proposed various structures of the dyes. As the result of this, there have been put into practice at present those dyes which have attained a level of considerable satisfaction.
However, in those dyes having blue type color tone among the reactive dyes, those having generally excellent characteristics have not yet to be found.
For example, there has been known the reactive dyes consisting of formazan type compounds having a structural formula as shown below (vide: Japanese Unexamined Patent Publication No. 4783/1981 and Japanese Unexamined Patent Publication No. 15451/1984).
While these dyes are suitable for use under the ordinary conditions for dyeing cellulosic and nitrogen-containing fibers, they are not satisfactory in every aspect of color fastness to washing, color fastness to perspiration and sun light, and further, acid stability. ##STR2## (Japanese Unexamined Patent publication No. 4783/1981) ##STR3## (Japanese Unexamined Patent Publictaion No. 15451/1984)
On the other hand, with diversification of the fiber materials, there have become used blended fibers of, for example, cellulosic fibers and polyester fibers. As the method of dyeing such blended fibers, there has conventionally been adopted a so-called "double-step method", wherein polyester fibers are dyed in advance at a high temperature of 120.degree. C. to 140.degree. C. or so by use of a disperse dye, and then cellulosic fibers are dyed at a low temperature of 60.degree. C. to 70.degree. C. or so by use of a reactive dye. On the other hand, there has recently been proposed a method of dyeing cellulosic fibers and polyester fibers simultaneously in a dye bath at a higher temperature of from 120.degree. C. to 140.degree. C. by a single-bath-and-single-step dyeing method, wherein the reactive dye and the disperse dye are used together. However, when a known reactive dye is used in this dyeing method, the reactive fixing rate of the dye to the cellulosic fibers is low and its build-up property is poor, with the consequence that no favorable dyed article can be obtained. As the reactive dye suitable for such single-bath-and-single-step dyeing method, there have been known those reactive dyes consisting of formazan compound to be represented by the following structural formula (vide: Japanese Unexamined Patent Publication No. 90264/1985). However, even when this reactive dye is used, the dyed article is not satisfactory in percentage exhaustion and build-up property. ##STR4##